I am not an expert but got good reviews on amazon and elsewhere
http://www.amazon.co.uk/Sennheiser-II-Precision-Isolating-Earphones-Black/dp/B001EZYMF4

There great for that price, virtually no feed back from the cords. I use them for the gym regularly and paid £35 two yrs ago.
http://www.whathifi.com/sennheiser/cx-300-ii/review

What other sets have you tried? Voted hot because it's a good price for these, but I personally found them the worst budget earphones I've tried so far. I've only tried 4 sets in the sub £20 bracket. IMHO

1. Musical Fidelity EB33 (£19.99)
2. Xiaomi Piston 3 (£7.50)
3. Soundmagic E10 (£19.99)
4. Sennheiser CX300II (£15.99)

The Musical Fidelity are hard to find at this price but they do pop up every now and then. The others are all available at the prices above and fairly close on quality, just down to personal preference. For me, the pistons are the best of the rest, and at £7.50 fantastic value.

Ignore them then. There are plenty of reviews on the web for these headphones if you'd rather not rely on user reviews (http://www.techradar.com/reviews/audio-visual/hi-fi-and-audio/headphones/sennheiser-cx-300-95423/review for example)

I see.

I have only used CX300 II before, not CX300. Do not know about CX300